During manufacture, rolled strips and sheets can be provided with a particular surface structure in a final rolling pass, in particular a final cold rolling pass. A roll stand is thereby used in which at least one of the work rolls of the roll stand has a defined surface structure which is impressed in the surface of the strip or sheet by the rolling pass.
A surface structure of this type can prepare the strip or the sheet for a particular form of further processing. Particularly in automotive engineering, but also in other fields of application, for example aircraft construction or rail vehicle construction, metal sheets are required which exhibit a very good forming behaviour and which make high degrees of deformation possible. In automotive engineering, typical fields of application include bodywork and chassis components. Moreover, in the case of visible, painted components, for example externally visible bodywork panels, the materials must be formed in such a way that the surface is not affected by faults such as slip lines or roping after spraying. This is for example particularly important in the case of metal sheets used to produce engine bonnets and other bodywork components of a motor vehicle.
Only slight pass reductions take place during a roll-embossing pass. The forming behaviour of the strip with the specific surface structure introduced through the roll-embossing pass, in other words the rolling pattern created through the embossment rolling, is also advantageously influenced through the embossing pass. For example, if the strip, or a sheet produced from the strip, is formed during the course of further processing, the surface structure of the strip introduced during rolling reduces the friction between sheet and forming tool. In particular, the surface structure is preferably designed such that the sheet can be wetted more effectively with lubricants during forming. The surface can have depressions in the form of lubrication pockets which can hold lubricants. This further reduces the frictional forces during forming and makes higher degrees of deformation possible.
However, in order to achieve this, there must be a possibility of adjusting the surface structure of the strip or the rolling pattern. During rolling, particularly during roll-embossing with low pass reductions, it is in particular difficult to ensure a consistently uniform impression of the surface structure of the work rolls, in particular on both sides of the strip. One problem is that the work rolls of the roll stand are subject to wear, and thus during continuous operation have a surface structure which changes over time. In addition, the surface structure of the work rolls can, over time, pick up material from the strip or impurities and consequently lead to a rolling pattern which can change over time. On the other hand, the strip which is fed into the roll stand is usually subject to fluctuations, which makes it difficult to achieve a uniform rolling pattern. The fed strip can for example vary in dimensions such as thickness, width or also curvature, or in profile or also in strength, which in turn also allows the rolling pattern to vary during rolling.
Furthermore, in order to achieve a uniform surface structure of the strip on both sides it is in practice often necessary, depending on the rolling conditions and the stand design in a rolling train, to use different work rolls for the upper side and underside, in particular work rolls with different surface topographies. This complicates the provision of corresponding work rolls for the roll stand.
Therefore, in DE 44 24 613 B4 a roll stand is suggested which can be controlled with respect to the surface roughness of the produced strip. This control is effected by means of bending equipment on the work rolls which can control the bending of the work rolls and thus the surface structure over the width of the strip. However, one disadvantage here is that corresponding roll stands equipped with bending equipment are complicated in structure and thus less economical. In addition, a control of the surface structure is only possible over the width of the strip. Adjustment of the surface structure on the upper side and underside of the strip, for example in order to take into account different degrees of wear or grinding of the work rolls, is not possible.
An apparatus and a method for rolling a strip is also described in EP 0 908 248 A2 in which the upper side and underside of the strip and the respective work rolls are supplied with lubricant via separately controllable spraying devices. Any differences in the rolling pattern of the upper side and underside of the strip can be reduced through the dosing of the lubricant. This apparatus and this method are in need of improvement, in particular with regard to process reliability.
The present invention is therefore based on the technical problem of providing a method and an apparatus for rolling in which the surface structure of a strip can be controlled on the upper side and underside in a process-reliable manner and the disadvantages of the prior art avoided.